1. Technical Field of the Invention
This disclosure generally relates to a high voltage generator of a semiconductor device, such as a flash memory, and more specifically, to a multi-level high voltage generator capable of generating and outputting various high voltage levels using one charge pump.
2. Description of the Related Art
Generally, programming or erasing data in a flash memory requires a voltage with a relatively high voltage level (or high voltage). The flash memory achieves this high voltage by means of a high voltage generator that uses a charge pump.
FIG. 1 is a block diagram of a conventional high voltage generator. As illustrated in FIG. 1, the conventional high voltage generator includes a charge pump unit 100, a voltage divider unit 102, and a pump control unit 104. This high voltage generator raises an input voltage VI to a desired target voltage and outputs the same.
The charge pump unit 100 includes a number of pump circuits serially connected as illustrated in FIG. 2. Referring to FIG. 2, each of the pump circuits produces an output voltage that is raised with respect to an input voltage, and the output voltage becomes the input voltage for the next pump circuit connected in the series. In this case, the pump circuits raise voltage in response to a pump control signal OSC_1 inputted from a pump control unit 104. If the pump control signal OSC_1 is not inputted from the pump control unit 104, the individual pump circuits of the charge pump unit 100 do not perform a voltage raise operation.
The voltage divider unit 102 operates according to an external enable signal EN, and divides an output voltage VO of the charge pump unit to generate a divided voltage VD. The voltage level of the divided voltage VD is determined according to the resistance values of serially connected resistors within the voltage divider unit 102.
The pump control unit 104 generates a pump control signal OSC_1 for controlling a voltage raise operation of each of the pump circuits according to the divided voltage VD from the voltage divider unit 102, an externally applied reference voltage Vref, the control clock signal OSC, and the enable signal EN. That is, if the divided voltage VD is lower than the reference voltage Vref, an output voltage of the charge pump unit 100 does not reach the target voltage. Thus, the pump control unit 100 generates a pump control signal OSC_1 using a control clock signal OSC and transfers the pump control signal OSC_1 to each pump circuit to perform a voltage raise operation. Meanwhile, if the divided voltage VD is higher than a reference voltage Vref, the output voltage of the charge pump unit 100 reached the target voltage. Thus, the pump control unit 100 stops the voltage operation by not generating the pump control signal OSC_1.
However, the conventional high voltage generator in this structure may simultaneously generate a voltage having only one voltage level. Therefore, if a number of voltages having different levels is required, additional high voltage generators should be prepared according to the circumstances. This increases the overall circuit area required for the high voltage generator and an ability to achieve highly integrated devices is degraded.
Embodiments of the invention address these and other disadvantages of the conventional art.